在Xamarin.iOS中设置RootViewController后,NavigationController为null

Question

我正在使用Xamarin.iOS的故事板.DashboardViewController(一个UINavigationController)被设置为故事板中的初始视图.但是,在我的AppDelegate类中,FinishedLaunching方法有条件地检查用户是否需要在应用程序启动时登录.如果是这样,它会将"ViewController"(登录控制器)设置为RootViewController,否则它将实例化由故事板设置的初始视图控制器,即"DashboardViewController".这是FinishedLaunching方法的代码.

    public override bool FinishedLaunching (UIApplication application, NSDictionary launchOptions)
    {
        // Override point for customization after application launch.
        // If not required for your application you can safely delete this method

        Window = new UIWindow(UIScreen.MainScreen.Bounds);

        var storyboard = UIStoryboard.FromName("Main", NSBundle.MainBundle);

        bool isLoggedOut = true;
        UIViewController rootViewController;

        if (isLoggedOut)
            rootViewController = (UIViewController)storyboard.InstantiateViewController("ViewController");
        else
            rootViewController = (UIViewController)storyboard.InstantiateInitialViewController();

        Window.RootViewController = rootViewController;
        Window.MakeKeyAndVisible();
    }

验证用户的凭据后,以下代码会尝试将RootViewController再次设置回原始的"DashboardViewController"并显示该视图.这是从登录控制器完成的.

    partial void LoginBtn_TouchUpInside (UIButton sender)
    {
        var appDelegate = UIApplication.SharedApplication.Delegate as AppDelegate;
        appDelegate.SetRootViewController (dashboardViewController, true);
        this.PresentViewController (dashboardViewController, true, null);
    }

以下是AppDelegate中"SetRootViewController"的代码:

    public void SetRootViewController()
    {
        Window = new UIWindow(UIScreen.MainScreen.Bounds);
        var storyboard = UIStoryboard.FromName("Main", NSBundle.MainBundle);

        bool isLoggedOut = false;
        UIViewController rootViewController;

        if (isLoggedOut)
            rootViewController = (UIViewController)storyboard.InstantiateViewController ("ViewController");
        else 
            rootViewController = (UIViewController)storyboard.InstantiateViewController (viewController);

        Window.RootViewController = rootViewController;
        Window.MakeKeyAndVisible();
    }

到目前为止,这是有效的,但如果我尝试在DashboardViewController(这是一个UINavigationController)中向堆栈中添加另一个视图,请使用以下代码从按钮单击,

    partial void ProfileBtn_TouchUpInside (UIButton sender)
    {
        this.NavigationController.PushViewController (profileViewController, true);
    }

NavigationController为null,应用程序崩溃.因此,此场景的基本流程是"将RootViewController设置为"ViewController",以便用户可以登录 - >当用户登录时,将RootViewController设置回DashboardViewController并显示该视图 - >单击按钮导航到另一个从DashboardViewController视图查看,但DashboardViewController中的NavigationController为null.

我究竟做错了什么？？任何帮助或建议将不胜感激(我为长期问题道歉).

Answer 1

我已决定将这个问题留给那些可能遇到同样问题的人.我已经找到了我认为的解决方案.在我的AppDelegate"SetRootViewController"方法中,而不是说,

Window.RootViewController = rootViewController;

我需要说,

Window.RootViewController = new UINavigationController(rootViewController);

其他一切都保持不变.工作流程现在按预期工作.这是因为我试图设置为RootViewController的控制器不仅仅是一个UIViewController,它是一个由UINavigationController包装的UIViewController.这个答案也在以下链接中重申

https://forums.xamarin.com/discussion/23424/how-can-i-use-this-navigationcontroller-on-my-view

我为回答我自己的问题而道歉,如果有人有更好的方法或者看到有问题,请告诉我.希望这可以帮助将来的某个人.